Electrostatic chucks are used as means to adsorptively hold down an adsorption target material (such as a semiconductor wafer or a glass substrate) in substrate processing devices that perform etching, chemical vapor deposition (CVD), sputtering, ion implantation, ashing, exposure, inspection, and the like.
There is a risk here that particles will be generated if the adsorption target material rubs against the mounting face of the electrostatic chuck. Further, increasing the contact surface area between the mounting face of the electrostatic chuck and the adsorption target material may lead to poor adsorption/desorption responsiveness of the adsorption target material.
Therefore, techniques are known that improve adsorption/desorption responsiveness of the adsorption target material while suppressing particle contamination by reducing the size of the contact surface area by providing protrusions on the mounting face side of the electrostatic chuck.
Furthermore, in addition to providing protrusions on the mounting face side of the electrostatic chuck, a technique is proposed for buffing the top face of the protrusions to form a planar surface where the top face has a surface roughness of not more than 0.25S (see Patent Literature 1).
The technique disclosed in Patent Literature 1 mirror polishes the top face and side surface of the protrusions as well as the planar surface around the protrusions (bottom surface of the recess) such that the generation of particles can be suppressed even when the underside of the adsorption target material contacts these areas (see [0008], [0029], and [0035] of Patent Literature 1).
However, if the top face of the protrusion is made to be a planar surface, particles may be increased instead due to the underside of the adsorption target material rubbing against the planar surface of the top face. Particularly in recent years, there has been a trend in which the restriction on the number of particles attached to the underside and the like of the adsorption target material has become more strict leading to concerns that flattening the top face of the protrusion can no longer address the restriction in the number of particles.
Note that flattening the top face of the protrusion may worsen the adsorption/desorption responsiveness of the adsorption target material.
Further, in addition to providing a protrusion on the mounting face side of the electrostatic chuck, a technique is proposed for shot-blast processing the top face of the protrusion to form a rough surface region in which the center line average roughness Ra on the top face is not less than 0.5 μm (see [0035] and [0043] for Patent Literature 2.
This rough surface region is provided to improve the uniformity of the in-plane temperature of the adsorption target material and to improve the adsorption/desorption responsiveness of the adsorption target material. Further, because the rough surface region is a non-contacting face that does not contact the underside of the adsorption target material, rubbing between the rough surface region and the underside of the adsorption target material can be suppressed (see [0011] and [0014] of Patent Literature 2).
However, a smooth region is formed in which the center line average roughness Ra around the rough surface region is not more than 0.5 μm. In other words, similar to the technique disclosed in Patent Document 1, there is a risk of increasing the particles by the underside of the adsorption target material rubbing against the smooth region of the top face. Particularly in recent years, there has been a trend in which the restriction on the number of particles attached to the underside and the like of the adsorption target material has become more strict leading to concerns that providing a smooth region on the top face of the protrusion can no longer address the restriction in the number of particles.
Note that providing a smooth region on the top face of the protrusion may worsen the adsorption/desorption responsiveness of the adsorption target material.
Further, when the protrusion is formed using a sand blast method or the like, a defective part such as a crack may be generated in the surface region of the protrusion or the surface region of the planar surface part. When these types of defective parts exist in the surface region, a part of the surface region desorbs as a base point of the defective part with the risk of generating particles.
These types of defective parts that reside in the surface region cannot be removed by buffing, and use of grinding processing methods, laser engraving methods, shot blasting methods, and the like have the risk of further increasing defective parts.
Further, there is a risk of increasing particles if no consideration is given to the crystal grain diameter of the material that configures the top face or side surface of the protrusion as well as the planar surface part in the periphery of the protrusion.
Further, if the rough surface region disclosed in Patent Document 2 is formed using a grinding processing method, laser engraving method, shot blasting method, and the like, thin and deep holes will be formed. Removing micro foreign objects trapped in this type of hole by cleaning is difficult, and there is a risk that a clean state of the electrostatic chuck surface cannot be easily recovered.
The trapped micro foreign object may float up from the rough surface region on account of an electric field generated at the time of operating the electrostatic chuck and it may adhere to the underside of the adsorption target material. In other words, because removing the micro foreign object trapped in the rough surface region is difficult by cleaning, any remaining foreign object may become a particle.